Characteristics Of Grain Size, Element Geochemistry And Their Implication Of Regional Sand-dust Accumulation System In North Of Jiangxi

The regional sand-dust accumulation system of Poyang Lake in North Jiangxiduring the last glacial is a regional response that in the glacial climate condition thewinter monsoon strengthen, sea level greatly reduced, causing the flood plains of theYangtze River and the Gan River exposed. That sand hill-Xiashu soil accumulationsystem is similar to the desert-loess accumulation system in Northern.But because ofits low latitude, the winter monsoon for the handling power significantly less than inthe north, and the provenance range is narrow, so the scale of sand-dust accumulationsystem is far less than the north desert-loess system.Due to the source of sand is linear,and restricted by local landform, local sand-dust accumulation system is divided intoseveral relatively independent subsystem.Based on the field work of the southwest of Poyang Lake, the west side of GanRiver downstream,we chose the Houtian-Daguling section as the study area. Thesection was set nine sedimentary sections along with the modern direction of wintermonsoon.It includes the flood plain section, sand hill section and Xiashu soilsection.This paper only focuses on the yellow-brown Xiashu soil located in uppersections（since the last glaciation）, on the lower reticulate red clay temporarily notinvolved.The section analysis is used to test a total of65samples.In this paper we usesedimentology and geochemistry method to analysis of samples in the study area,including the analysis of granularity characteristics and the constant elementcharacteristics.The article draw the following conclusions:(1) Grain size frequency curves of the Houtian-Daguling section denotes particlesize tapering, fine particles peak increases gradually and coarse particle peakgradually shrinking from north to south. And in the end of section found yellow clay.From the point of spatial distribution, sedimentary facies of this section transmit fromsand dune in Houtian sand hills~sand loess~clay loess from Fengcheng to Dagulinghills to loess clay in Daguling hill along with the modern direction of wintermonsoon.In that process, the grain size composition and parameters show a systematicchange from north to south with logarithmic function mode of the distance to HoutianGan River valley. Within the distance of20km, they change violently, but out of thisdistance, will be asymptotically stable. Thus, the distance might be a characteristicsone. (2)The constant element geochemical analysis results show that theHoutian-Daguling section sediment element enrichment and loss performance arecoincidence. Along the winter monsoon direction the wind weathering intensitychange from medium to strong. Element ratios of obvious gradient phenomenonindicate that two kinds of eolian characteristics of sedimentary formation, it alsoindicate the Poyang Lake area of desert sand, Xiashu soil for proximal accumulation,over bank deposits as the upper hand in the direction of the Gan river valley.(3) The regional sand-dust accumulation system of the Houtian-Dagulingsection as a product of the last glacial, which formation mechanism is: under thestrong regional winter monsoon the coarse particle material of floodplain of GanRiver valley accumulation formed sand hill near the source area on the downwinddirection,and fine particulate matter moved to the further accumulation.